A conventional portable drill having an electromagnetic base is shown in FIGS. 1 and 2. The electromagnetic base is designated 1. The alternating current rectifier for the base power supply is designated 2. The base 1 is applied to the workpiece to be drilled 8. On the drill stand is a slide support 3 which includes a dovetail groove open at both ends in which a rack slide rod 6 moves to and from the workpiece and supports the electric drill head 7. The rack gear t is driven by a spur gear 5 on rotating the journalled three arm handle 4.
When the portable electromagnetic drilling machine is applied to a workpiece 8 to be drilled, as seen in FIG. 2, chips 9 are generated by the drill bit, near the area P below the slide support 3 and the rack slide rod 6. To avoid damage to the drill stand from chips, particularly damage to the slide rod 6 and the dovetail groove in support 3, prior art construction limited the extent of the support 3 in the direction of the workpiece to about half the distance from the highest level of the drill head to the workpiece. This is shown in FIG. 1 as H/2. Thus the support 3 ends high above the workpiece 8.
A disadvantage of the above construction is seen when the handle 4 is turned to lower the electric drill 7 and the drill bit is not guided in a stable path to engage the workpiece 8 with maximum accuracy.
In a conventional portable electromagnetic drill stand the electromagnetic base 1 is of comparatively large size to provide stability.
An advantage of a large electromagnetic base is that heat is disapated from the insulation around the electromagnet coils and this avoids early burnout of the coils. On the other hand a large magnetic base prevents having a machine of small compact size and moreover may make handling inconvenient.